Researchers in South Korea studied over 3,400 pregnant women to understand how smoking affects gestational diabetes—a type of diabetes that develops during pregnancy. They found that women who smoked before or during early pregnancy had a much higher risk of developing the more serious form of gestational diabetes that requires insulin treatment. The more a woman smoked (measured in pack-years), the greater her risk. Even secondhand smoke exposure showed a potential link to gestational diabetes. These findings suggest that quitting smoking and avoiding secondhand smoke during pregnancy could significantly reduce a woman’s risk of developing this serious pregnancy complication.

The Quick Take

  • What they studied: Whether smoking before and during early pregnancy increases the risk of gestational diabetes (a blood sugar problem that happens during pregnancy) and how severe it becomes
  • Who participated: 3,457 pregnant women in South Korea who were followed from 2013 to 2017. All were Korean, carrying single babies, and had no diabetes before pregnancy
  • Key finding: Women who smoked during early pregnancy were nearly 10 times more likely to develop the serious form of gestational diabetes that requires insulin shots. The risk increased dramatically with how much they smoked—women with heavy smoking histories had 20-26 times higher risk
  • What it means for you: If you’re planning to get pregnant or are already pregnant, quitting smoking (or avoiding secondhand smoke) could significantly lower your chances of developing gestational diabetes. This is especially important because the serious form requires medication and poses greater health risks

The Research Details

This study used data that researchers had already collected from pregnant women in South Korea over several years (2013-2017). Instead of starting fresh, scientists looked back at the existing information to answer new questions about smoking and gestational diabetes. They compared women who smoked to those who didn’t, and tracked which women developed gestational diabetes and how severe it was. The researchers carefully adjusted their analysis to account for other factors that might affect diabetes risk, like age and weight, so they could focus specifically on smoking’s effects.

By studying real-world data from thousands of women followed throughout their pregnancies, researchers could see actual patterns and connections that might not show up in smaller studies. This approach is stronger than just asking people to remember their smoking habits because the information was collected as it happened. The researchers also looked at different levels of smoking intensity, which helps show whether a little smoking is safer than a lot—or if any amount poses a risk.

This study is fairly reliable because it followed a large number of women (3,457) and collected information before outcomes occurred, reducing memory errors. The researchers excluded women with existing diabetes and other complications to focus on the specific question. However, the study only included Korean women, so results may not apply equally to other populations. The number of women who developed the serious form of gestational diabetes (33 cases) was relatively small, which means some findings have wider ranges of uncertainty

What the Results Show

Among the 3,457 pregnant women studied, 231 developed gestational diabetes (about 7%). Of these, 198 had the milder form controlled by diet alone, and 33 had the more serious form requiring insulin. The most striking finding was that smoking during early pregnancy dramatically increased risk of the serious form: women who smoked were nearly 10 times more likely to need insulin treatment compared to non-smokers. Smoking before pregnancy also increased this risk, though not quite as much (about 4 times higher). Importantly, smoking did not significantly increase the risk of the milder, diet-controlled form of gestational diabetes.

The study revealed a clear dose-response relationship, meaning the more a woman smoked, the higher her risk. Women who had smoked more than 4 pack-years (roughly equivalent to smoking one pack per day for 4 years, or 2 packs per day for 2 years) had dramatically elevated risk—about 20 times higher for the serious form. Even higher smoking amounts (4-6 pack-years and over 6 pack-years) showed similarly extreme risk increases. Among women who never smoked, secondhand smoke exposure showed a borderline association with overall gestational diabetes risk, suggesting it might be harmful but the evidence wasn’t quite strong enough to be certain

This research adds important new details to existing knowledge about smoking and pregnancy complications. Previous studies have shown smoking harms pregnancy, but this study specifically clarifies that the most serious impact appears to be on insulin-requiring gestational diabetes rather than milder forms. The dose-response relationship (more smoking = more risk) aligns with how smoking affects other health conditions and strengthens the evidence that smoking itself, not just coincidental factors, causes the increased risk. The finding about secondhand smoke suggests even non-smokers face potential risks, though more research is needed to confirm this

The study only included Korean women, so findings may not apply equally to other ethnic groups who might have different genetic risks or smoking patterns. The number of women with serious gestational diabetes was relatively small (33 cases), which means the confidence ranges around the risk estimates are quite wide—the true risk could be somewhat higher or lower than reported. The study couldn’t prove that smoking directly causes gestational diabetes, only that the two are associated. Some women may have quit smoking during pregnancy, which wasn’t fully captured in the analysis. Additionally, the study relied on self-reported smoking information, which could be underestimated if women didn’t fully disclose their smoking habits

The Bottom Line

Women planning pregnancy or currently pregnant should strongly consider quitting smoking, as the evidence shows a clear and substantial increase in serious gestational diabetes risk (HIGH confidence for active smoking; MODERATE confidence for secondhand smoke). Even women who never smoked should try to avoid secondhand smoke exposure during pregnancy. Healthcare providers should prioritize smoking cessation counseling as part of prenatal care, as this intervention could prevent a significant pregnancy complication

This research is most relevant to women of childbearing age, especially those planning pregnancy or currently pregnant. It’s particularly important for women who smoke or are regularly exposed to secondhand smoke. Healthcare providers, public health officials, and pregnancy educators should use this information to strengthen smoking cessation programs. Partners and family members of pregnant women should also pay attention, as their smoking creates secondhand smoke exposure that may affect pregnancy health

Gestational diabetes typically develops in the second or third trimester of pregnancy, so the protective effects of quitting smoking would likely appear within weeks to months of stopping. However, the best approach is to quit before becoming pregnant if possible, as this study shows smoking before pregnancy also increases risk. If a woman is already pregnant and smoking, quitting immediately could still reduce her risk compared to continuing to smoke

Want to Apply This Research?

  • Track smoking status and secondhand smoke exposure weekly during pregnancy planning and throughout pregnancy. Users can log: cigarettes smoked per day (if applicable), quit attempts and dates, secondhand smoke exposure duration and location, and any pregnancy-related glucose screening results when available
  • Set a specific quit date and use the app to track daily progress toward zero cigarettes. For users exposed to secondhand smoke, set goals to spend less time in smoking environments (e.g., ‘avoid smoky venues 3+ days per week’). Users can log triggers that make them want to smoke and develop alternative coping strategies within the app
  • Create a long-term tracking dashboard showing: days/weeks smoke-free, reduction in secondhand smoke exposure, and correlation with any glucose monitoring results from prenatal care. Set monthly milestones toward complete smoking cessation. Include reminders about upcoming glucose screening appointments and links to smoking cessation resources

This research shows an association between smoking during pregnancy and increased risk of gestational diabetes, but individual risk varies based on many factors. This information is for educational purposes and should not replace personalized medical advice from your healthcare provider. If you are pregnant or planning pregnancy and smoke, please discuss smoking cessation strategies with your doctor or midwife. If you have been diagnosed with gestational diabetes, work closely with your healthcare team on management and treatment. Pregnant women should not attempt to quit smoking abruptly without medical guidance, as this requires careful planning and support.